Minimally invasive surgical interventions have gained steadily in importance for years and are indispensable for example for the treatment of stenoses. Recently, they have also been used increasingly in the implantation of artificial heart valves. Suitable delivery catheters are known in a very wide range of designs and are the subject of on-going further development. In recent years, the development has focused particular attention on catheters which not only permit the initial placement, but also the removal or positioning of cardiovascular implants.
Delivery catheters of this type typically consist fundamentally of a first, inner catheter shaft, at the distal end of which there is arranged the implant. The implant and the first, inner catheter shaft are surrounded by a second, outer catheter shaft. The distal region of the second outer catheter shaft, which surrounds the implant, is often referred to as an implant capsule, or occasionally as a catheter sleeve. The implant capsule can consist of the same material as the second outer catheter shaft or of another material connected to the second outer catheter shaft. “Proximal” denotes a part of the delivery catheter disposed closer to the operating surgeon, and “distal” accordingly denotes a part of the delivery catheter disposed further away from the operating surgeon.
The implants are often constructed using a shape-memory material. In these cases, the implants are held in their compressed form by the catheter sleeve surrounding them as they are delivered to the site of implantation. By displacing the catheter sleeve, for example proximally, the retaining force exerted onto the implant by the catheter sleeve disappears and the implant expands.
Recently, solutions have been proposed to permit a return (resheathing) of an already released implant into the delivery catheter, i.e. especially into the implant capsule. Such solutions are very much welcomed by the operating surgeons because they permit corrections during the delivery process and thus help the implantation process to be concluded with the best-possible result. Especially with retraction of heart valve stents into the implant capsule, or, more specifically, as the distal catheter end is drawn back over the stent, relatively high reaction forces occur. These forces and stresses lead to complex problems, as described by way of example in the prior art description in US 2011/0098804 A1, and are linked to the search for a (partial) solution.
It is known to produce the catheter tip from a soft/atraumatic material to avoid injuries to the vessel walls as the catheter device is advanced. The soft material is intended to afford sufficient protection of the sensitive vessel inner wall and the natural aortic valve when an aortic valve replacement catheter is passed therethrough. In the event of very sharp bends of the transition region between distal catheter tip and adjoining outer tube (capsule containing the implant), it can be that edges are exposed which might injure the vessel inner wall or the natural aortic valve. Particularly in systems of the above-mentioned type which can recapture a partially released implant, the catheter components are heavily loaded, which can lead to an even more pronounced edge formation. The reason for this pronounced edge formation is the funnel-shaped expansion of the capsule by the return by way of the partially released implant. There is an enlarged peripheral edge at the distal catheter end.